This invention relates to the surface treatment of metal articles and is particularly concerned to provide an improved means of identifying and repairing faults at or near the surface of metal.
The invention is particularly useful in the identification and removal of blemishes, cracks, tears and inclusions at or below the surface of articles of hot semi-finished continuous cast products. Typically such products are to be hot rolled into sheets or the like. Unfortunately the semi-finished products can have visible (or invisible) defects or weak points, in or immediately below the surface, e.g. fissures, tears, folds or the like. If these are carried into the rolled products rejects will arise and even damage of the surface of the roller cylinders can occur. It is thus usual to inspect the semi-finished product before proceeding with the rolling, to determine whether they can be rolled directly or whether they must be treated beforehand to move or repair the defects which they have, or even if they are of such low quality that they must be rejected and recycled.
Because the semi-finished products are hot, an observer cannot examine them directly. There have been a number of proposals based on the principle of forming an image of the defects from a distance which will then save as a guide for the repair of the surface usually by machine or hand operated scarfing.
In U.S. Pat. No. 5,071,105, for example, there is described a scarfing torch to remove blemishes from the surfaces of steel billets, ingots and the like in which the torch is fitted with a nozzle having a visual observation optical device extending co-axially inside a central gas feed pipe and situated a specific distance from the main orifice of the nozzle so that the bounds of its angle of view pass through the edges of the main orifice.
U.S. Pat. No. 4,615,877 describes a method of striping hot steel slabs in which an optical pyrometer 41 is mounted on a vertical bracket 38 and is directed toward a surface of a metal slab 12. The bracket 38 is mounted upon a reciprocating beam 32 to which a scarfing torch 36 is similarly mounted. To effect a maximum sensitivity and accuracy of the pyrometer 41, it is focused on the area near the leading edge of the molten puddle of metal created by the scarfing torch. The pyrometer is arranged to detect flashes, and testing has shown that accurate focusing of the pyrometer is critical to operation of the apparatus of pick up all flashes as they occur.
U.S. Pat. No. 4,671,674 discloses a process for the detection of weak points or defects on steel semi-finished products, in which a gantry has a blowtorch and a camera mounted thereto. The camera is able to view the image of the points of application of the torch flame. The document concerns a process where detection and repair are separate operations, undertaken by separate operatives. This method does not lead to a fast and reliable detection and repair process.
JP-A-59174275 describes a process in which a camera appears to be focused onto a point in the molten metal bath generated by the scarfing torch. The camera is not mounted on the torch and does not appear to have a field of vision greater than and encompassing the area of the molten metal bath.
JP-A-10118756 relates to a hot scarf control device in which pre and post scarfing CCD cameras are provided. The first determines the slab stop position and the second (or post-scarf) identifies the state of the slab immediately after scarfing. Neither of the cameras appear to be mounted on the torch.
BE-A-895665 (which is equivalent to U.S. Pat. No. 4,601,762) describes a method for conditioning metal products in which the detection and scarfing devices are separate entities. The monitoring device is similarly separate and no information is provided as to their particular orientation.
It is one object of the present invention to provide a method and an apparatus in which their particular orientation.
It is one object of the present invention to provide a method and an apparatus in which the field of vision surveyed by an optical device associated with a gas torch can be greatly enhanced and to provide a method of removing surface defects from the metal article by a continuous process of observation, identification and removal.
Accordingly, in one aspect the invention provides a method detecting and removing defects from metal articles by scarfing, the method comprising the steps of:
directing an optical viewing device which is mounted on a scarfing torch to view the hot surface of the metal article to be scarfed and to locate defects and identify them by area and depth;
adjusting the position of the torch according to sensed data to scarf away the defects;
recoding the defects and the scarfed area;
characterised by the optical viewing device is arranged to view an area greater than and including that area of the metal surface which is scarfed upon operation of said scarfing torch.
Preferably the scarfing torch supplies flame to overheat the surface of the metal to be scarfed so that the overheated metal produces flashes of high intensity light which are sensed by the optical device and are identified as defects to be scarfed. These are then photographed to record the defects. This step may be in the form of a first scarfing pass
Preferably the size of the flash is used to determine the size of the defect. Also, the shape of the flash of light is used to identify the nature of the defect. Specific shapes and their meaning is set out below.
Most preferably the method includes the step of moving the torch along successive wide generally parallel passes.
Typically the defect detection and elimination is performed on long, flat, metallic products at an ambient or elevated temperature produced either by ingot casting or a continuous casting apparatus.
It is a feature of the invention that the method involves analysing the hot bath of molten metal using a camera following the scarfing operation to provide an image to be reviewed by an operator.
The image can be used to give a real time picture which can be analysed by an operator or by comparator means.
In practice, the metal article, typically a hot slab, is placed at a scarfing station and then scarfed. This creates a bath of molten metal as the surface metal is removed, and the optical viewing device tracks the scarfed surface and takes photographs of the high intensity flashes of light created by the effects which remain after the initial scarfing. A map of the surface of the slab has previously been created, and the photographs are compared to the map to establish where the defects remain. The flashes of the light recorded on the photographs identify the nature of the defects, so the operator can readily carry out a secondary scarfing for local treatment, i.e. removal of these By the method of the invention defects can be identified and removed in one continuous operation which can proceed at a speed compatible with that of a continuous casting operation and, because of the external mounting of the optical device adjacent the torch, a wide surface area can be seen at any one time. This enables the operator to locate defects over a wide area and treat them readily.
According to the invention in another aspect there is provided apparatus for the detection and elimination of defects on metal articles, the apparatus comprising a scarfing torch to melt a localised region of the surface of the metal to provide a bath of molten metal, an optical viewing device mounted externally on the scarfing torch and a computer controlled means to quantify and qualify the defects detected in the bath of molten metal, the defects being removable by action of said torch, characterised in that the optical viewing device is arranged to provide, in use, a field of vision greater than an embracing the bath of molten metal.
Preferably the apparatus includes means to analyse the image provided by the optical device in the form of flashes of light, and to classify these are defects according to size and depth of defect and optionally by nature (crack or inclusion) and number.
It is preferred that the apparatus includes means to provide instructions for positioning the torch, to create into a map of the locations of the defects.
It is much preferred that the torch has a generally circular front face having multiple flames enabling simple defect detection by a simple single movement of elimination by large passes and the torch includes means for instantaneous change from one operating processes to another.
Preferably the apparatus has means to process both television type and industrial type images at a speed of 25 or 30 images per second, in colour or black and white
The optical device may be connected to a visual display unit remote from the hot metal article whereby an operator can observe the localised region of the surface and react to any visual defects shown by appropriate scarfing using the torch. The optical device may be a video camera or CCD camera (charge coupled device) to transmit images to a remote, operator-viewed screen or to a microprocessor-controlled automated system. The optical device may be in the form of an array of optical fibers connected to a remote control system. The optical device may be connected to computer-controlled means to interpret the signals received, identify defects and control movement of the scarfing torch to remove defects in direct response to the signals received. The apparatus may also include a video cassette recorder or the like for a permanent record.
The optical device may be mounted, for example, on a frame beneath which the metal article to be treated is passed. If desired, the optical device and the torch may be mounted to travel along their supporting frame so that they can be moved transversely across the metal surface passing beneath them. This option is particularly useful where semi-finished metal products are of considerable width, e.g. up to several metres. Alternatively, it may be necessary install a multiplicity of torches and optical devices on the frame spanning the metal surface.
Preferably the camera operated vision system causes a permanent picture of the bath while the blow torch is operated. The image is optimised to visualise the useful zone in the field of vision of the camera in order to detect defects (in the bath, both for defects with lower and greater depth than that of the bath pattern).
The parameterization of the camera shooting conditions is adapted to the types of defects which are expected to be found on the basis of the product development data analysis (shutter adapted to a micro-inclusions for example).
The photograph device is automatically adjusted to the bath image for both cold and hot slabs at a temperature up to 1000xc2x0 C. and over.
The image processing system preferably
sets the reference point in relation to the bath for defect detection.
records at any time the position of the point of reference in relation to the product to establish a map of the defect locations.
selects automatically the xe2x80x9cinterestingxe2x80x9d zones for defect detection on the bath image (classified as: shallow, fairly deep, very deep and located at the rear of the bath). The depth is actually linked to the measurement of the bath pattern. In one preferred embodiment of the system, 4 distinct zones have been isolated and analyzed one by one.
detects the flashes of light by contrast on the basis of the average level of grey thresholds for the zone in question.
distinguishes flashes of light indicative of defects from flashes of light produced by dust particles coming into the camera""s field of vision.
counts the number of defects in the zone in question.
measures the coordinates of each defect on the basis of two reference axes.
records the shape and the surface of the defects for comparison with those previously encountered and recorded.
compares the evolution of the flashes with a similar reference axis on all successive images where they appear in order to confirm the nature of defects.
The image processing system both images recorded from the detection operation images recorded from the defect elimination operation.
The system can process simultaneously images taken on the basis of different filming parameters to both detect and eliminate gross and tiny defects.